/*
 * Copyright 2021 Shulie Technology, Co.Ltd
 * Email: shulie@shulie.io
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package io.shulie.surge.data.runtime.disruptor;

import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;

import static java.util.Arrays.copyOf;

/**
 * Provides static methods for managing a {@link SequenceGroup} object.
 */
class SequenceGroups
{
	static <T> void addSequences(final T holder,
			final AtomicReferenceFieldUpdater<T, Sequence[]> updater,
			final Cursored cursor,
			final Sequence... sequencesToAdd)
	{
		long cursorSequence;
		Sequence[] updatedSequences;
		Sequence[] currentSequences;

		do
		{
			currentSequences = updater.get(holder);
			updatedSequences = copyOf(currentSequences, currentSequences.length + sequencesToAdd.length);
			cursorSequence = cursor.getCursor();

			int index = currentSequences.length;
			for (Sequence sequence : sequencesToAdd)
			{
				sequence.set(cursorSequence);
				updatedSequences[index++] = sequence;
			}
		} while (!updater.compareAndSet(holder, currentSequences, updatedSequences));

		cursorSequence = cursor.getCursor();
		for (Sequence sequence : sequencesToAdd)
		{
			sequence.set(cursorSequence);
		}
	}

	static <T> boolean removeSequence(final T holder,
			final AtomicReferenceFieldUpdater<T, Sequence[]> sequenceUpdater,
			final Sequence sequence)
	{
		int numToRemove;
		Sequence[] oldSequences;
		Sequence[] newSequences;

		do
		{
			oldSequences = sequenceUpdater.get(holder);

			numToRemove = countMatching(oldSequences, sequence);

			if (0 == numToRemove)
			{
				break;
			}

			final int oldSize = oldSequences.length;
			newSequences = new Sequence[oldSize - numToRemove];

			for (int i = 0, pos = 0; i < oldSize; i++)
			{
				final Sequence testSequence = oldSequences[i];
				if (sequence != testSequence)
				{
					newSequences[pos++] = testSequence;
				}
			}
		} while (!sequenceUpdater.compareAndSet(holder, oldSequences, newSequences));

		return numToRemove != 0;
	}

	private static <T> int countMatching(T[] values, final T toMatch)
	{
		int numToRemove = 0;
		for (T value : values)
		{
			if (value == toMatch) // Specifically uses identity
			{
				numToRemove++;
			}
		}
		return numToRemove;
	}
}
